Sewer systems inventoried

City turns to GIS to update utility maps

A Woolpert surveyor takes measurements and determines pipe sizes on a section of the sanitary sewer system in Alexandria's Old Town historic district. Attribute data was collected for both pipes and manholes—approximately 20 attributes per structure.

This surveyor determines flow direction and gathers as many attributes as possible on a curb inlet without a manhole. Data collection was sometimes a challenge for nonstandard historic structures in the city.

The historic city of Alexandria, Va., is abandoning its outdated hard-copy utility maps in favor of up-to-date sanitary, storm, and combined sewer geographic information system (GIS) maps created in the field, in real time.

Engineers in Alexandria—who spent the last few years collecting condition-assessment information and completing infiltration/inflow, sanitary sewer overflow, and National Pollutant Discharge Elimination System (NPDES) permitting projects—knew that the city ultimately needed a comprehensive, updated operating map showing the location and connectivity of its sanitary, storm, and combined sewer systems.

“We had mylar maps in flat files with utility sizes and locations, but these sewer maps hadn't been updated since the mid-1980s,” said Emily A. Baker, P.E., city engineer in the department of transportation and environmental services. “Records existed—development plans, infrastructure project drawings, as-builts, and hand sketches—but they weren't reconciled on the same map. That's been a problem for developers, maintenance staff, and our engineers who need to perform modeling to address capacity issues in areas with drainage and flooding problems.”

Baker said that city staff must direct developers, engineers, and the public to microfilm, as-built records, and development project archives if they need utility information for an area of the city. “Sometimes we have to send out a field crew,” said Baker. “The whole thing is a time-intensive process.”

City staff knew that a global positioning system (GPS) utility inventory was needed. By building a geodatabase data model and extending the city's existing GIS to include sanitary, storm, and combined sewer data, city staff knew they could better manage Alexandria's infrastructure and launch an improved maintenance, asset management, and work order management program.

Taking the Challenge

Such a project would be challenging for any city, but especially for one of America's oldest cities, located just outside Washington, D.C. Alexandria encompasses 15½ square miles and serves a population of 130,000. Approximately 540 acres of the city's Old Town historic district, established in 1749, is served by combined sewers, and some of these structures date back to the mid- to late-1800s. Since 1988, Alexandria has seen unprecedented commercial redevelopment; office complexes totaling more than 2 million square feet have been constructed, and numerous attractions in Old Town continue to draw as many as 1.5 million visitors annually.

Because of the city's aging infrastructure—which requires more maintenance and repairs—and all the redevelopment, map updates have not kept pace with rapidly changing field conditions. “Development is a big piece of what we do in Alexandria and an important reason why we need new sewer maps,” said Baker. The city, for example, requires that consultants show adequate capacity in existing systems before proceeding with a development project.

The city also knew it needed tools to keep maps updated in the future. So city staff worked with Woolpert Inc. staff in Arlington and Portsmouth, Va., to develop an infrastructure management GIS for sewers in the city. Woolpert used SmartSurveyor, specialized software for infrastructure inventory that allows real-time mapping in the field. Mapping-grade GPS equipment and pen-based handheld computers were used to collect feature locations and attribute data for pipes and manholes, approximately 20 attributes per feature. Using SmartSurveyor, Woolpert also:

Established connectivity and created the GIS on the fly to save post-processing time

Ran approximately 150 data validation rules, in the field and in real time, for optimum quality control. Any errors, such as incorrect pipe-to-structure or pipe-to-pipe connectivity, were flagged for immediate resolution in the field.